Power transmissions which transmit power by a belt disposed around a pair of pulleys have been well-known and are widely used. As such a transmission, a belt-type continuously variable transmission comprises a pair of pulleys, each pulley having a variable groove width, and a belt disposed therearound. The V-belt pitch radii of the pulleys are variably changed by adjusting the groove widths of the pulleys, so that the speed ratio of the transmission is continuously varied. It has been known that this type of transmission can be used on a vehicle as disclosed in Japanese Laid-Open Patent Publication No. H4(1992)-258528, which was filed by the same applicant as for this application.
This vehicular continuously variable transmission comprises a drive and driven pulleys, a belt, a forward-reverse selector mechanism, a starting mechanism, a reduction train, a differential mechanism, etc. in a hosing, and for lubricating these mechanisms, forced-feed lubrication or sprinkled lubrication by gear rotation is carried out. The oil used for this lubrication is also used as a hydraulic pressure controlling fluid (hydraulic oil) for controlling the adjustment of the groove widths of the drive and driven pulleys and for controlling a clutch.
The hydraulic pressure which is used for the forced-feed lubrication and for the hydraulic control is generated by a hydraulic pump which is driven by an engine through a gear or a chain mounted on a shaft that is coupled to the engine, and the hydraulic pressure is delivered to the components which require lubrication and to the components which require hydraulic pressure control. After the hydraulic pressure is used for the respective purposes, the hydraulic oil flows downward from the respective components. Therefore, the transmission includes an oil well or an oil pan to collect the hydraulic oil, which is then recirculated by the hydraulic pump.
In this vehicular transmission, the hydraulic oil, which has been used for forced-feed lubrication and hydraulic pressure control, flows on and along the inner surface of the housing, which accommodates the continuous speed change mechanism, the starting mechanism, the reduction train, the differential mechanism, etc. of the transmission, and the oil flows through an opening which is provided in the lower portion of the housing, to the oil pan. In the housing, the space for accommodating each mechanism is partitioned with a cover, or the wall of the housing is configured to partition the accommodation space for each mechanism. In this case, an independent oil outlet is provided in the accommodation space partitioned for each mechanism.
However, in this construction of the continuously variable transmission, the position of each mechanism, i.e., the above mentioned continuous speed change mechanism, the starting mechanism, the reduction train, the differential mechanism, etc. in the housing is not arranged evenly equidistant with respect to the oil pan, and the lubrication oil, after being used, comes out of the rooms which are partitioned for the respective mechanisms in different amounts. Therefore, the hydraulic oil returning from each mechanism to the oil pan joins in the way back and forms a complicated flow in the housing, which may tend to produce bubbles and vortices in the hydraulic oil in the oil pan. As a result, the lubrication oil which is sucked from the oil pan into the oil pump may include mingled air, which may cause a shortage in the real amount of lubrication oil that is supplied to each mechanism and a decline of the pressure that is needed for proper lubrication. Also, the oil may acquire a high temperature, which renders the oil to lose viscosity and less effective as a lubricant.